1. Field of the Invention
This invention relates to a punching tool and more particularly to a tablet making punch having one or more punches connected to a holder in a manner to assure precise connection of the punch to the holder for the tolerances required while permitting rapid changing of a punch on the holder.
2. Description of the Prior Art
Rotary type compressive tablet forming machines are well known in the art and, as illustrated in U.S. Pat. No. 3,483,831, are operable to compressively compact powder, granular and like material into compact tabletlike bodies. The tablets are applicable for the preparation of pharmaceutical, food, chemical and agricultural preparations. As disclosed in the above patent, a rotary-type compressive tablet forming machine includes a series of a plurality of press units. Each unit includes a stationary die with cooperating upper and lower punches. The upper punch is slidable into and out of a die opening within which the lower punch is guided. The press units are continuously moved along a predetermined path and the units are supported on a turntable, which is rotated so that the press units will be continuously moved along a circular path.
In the path of travel of the press units is positioned a pair of stationary upper and lower rollers counter-facing each other. As each press unit passes through the space between the upper and lower rollers, the upper punch engages the curved periphery of the upper roller and is thereby downwardly guided to slide into the upper die opening while the lower punch engages the curved periphery of the lower roller and is thereby upwardly moved to slide within the lower die opening. The material within the die opening is compacted to form a solid tablet.
As soon as the press unit has passed through the space between the rollers, the punches are disengaged from the respective rollers and the compression on the compact body by the punches is released. The upper punch is gradually guided upwardly so as to leave the die, and the lower punch is also guided upwardly to push the solid compact body out of the die opening. Thereafter, the die opening is charged again with new material, and the press unit is further moved to the position of the upper and lower stationary rollers, where the same operation is repeated.
Examples of known punches adaptable for use in tablet forming operations and punch press operations are described in U.S. Pat. Nos. 458,076; 1,507,783; 2,920,913; 2,927,492; 3,274,878; 3,759,130; 3,935,771; 4,007,653 and 4,339,976. An inherent problem in punching operations is the manner in which the punch or insert is removably secured to the holder so as to maintain the required tolerances to assure correct engagement of the punch and the die. It is critical that the punch be of a preselected length so as to extend a preselected distance into the die so that, for example in tablet forming, the required degree of compaction is obtained. After many cycles of use, the punches become worn and the required tolerances are no longer obtainable, requiring that the punches be removed and replaced on the holder.
In one well-known design, a detent arrangement is utilized for securing a punch insert in the punch holder. However, this is considered to be cumbersome because of the space taken up on the holder for the detent arrangement. A similar arrangement is also provided with the well known set screw arrangement for releasably securing a punch to a holder. These types of means for releasably securing a punch to a holder are undesirable because the required tolerances are difficult to maintain for the entire cycle life of the punch.
In the above-discussed tablet forming operation, both the upper and lower punches are similarly supported in punch holders and it is the conventional practice that the known dies include only a single hole because only a single punch is provided on each holder. This limitation is particularly imposed by the means by which the punch is secured to the holder, such as by detent or a set screw arrangement, so that insufficient area is available on the holder for accommodating more than a single punch.
Therefore, there is need, in tablet forming operations, for a punch which is releasably connected to a holder in a manner to facilitate rapid and precise replacement of a punch in the holder, particularly after the punch has become worn and the critical length of extension of the punch in the die is not within the required tolerance. The punch should be easily inserted and removed from the holder, while maintaining the required tolerances for the cycle life of the punch. Further, there is need to increase the productivity in tablet forming operations by providing a multiplicity of punches on a single holder, where each punch is easily inserted and removed and the required tolerances are maintained.